Within human sports science, practitioners and therapists regularly utilise exercise and training aids within the rehabilitation of neuromuscular disorders, informed by a comprehensive evidence base that has been developed through research (Gross et al., 2016). In equestrianism, despite increasing calls for evidence-informed practice, few studies have evaluated the impact of common exercises and training aids, such as the Pessoa Training Aid™ (PTA), used within rehabilitation and to train horses’ naïve to ridden work.

A fundamental goal of training or rehabilitation is to prepare the horse for the physical and mental demands exercise and/ or competition will place upon them. This is achieved through a combination of physiological conditioning to establish fitness and generate muscle mass (hypertrophy), alongside developing the motor skills to be able to complete specific movements required for different disciplines. The horse’s spinal, abdominal and pelvic musculature are fundamental structures which facilitate movement and function, and therefore influence equine performance, regardless of the equestrian discipline of the horse (van Weeren et al., 2010). Biomechanically these muscles work together to generate movement of the hindlimb and transfer the force and power created in the hindquarters, through a stable spine to provide the propulsion and power the horse requires to move, change gait and to perform effectively (van Weeren et al., 2010). Injury, lameness, ‘weakness’ or muscle hypotrophy, and pain can alter a horse’s biomechanics resulting in spinal and abdominal muscle spasm and/or inhibition (Zsoldas et al., 2010).

Figure 1: Low (B) position of the Pessoa Training Aid

Affected horses may present with spinal extension or a cranial pelvic tilt, both of which are undesirable postural characteristics that may impede function during movement reducing performance (van Weeren et al., 2010). Groundwork techniques, such as the utilisation of training aids including the PTA may be used to promote, maintain and restore the physical, psychological and social wellbeing of horses (Buchner and Schildboeck, 2006) and are often advocated by industry professionals to restore or prevent muscle related problems in the performance horse. To date, the majority of research in this field has examined the kinematic impact of working horses using various training aid systems, for example evaluating the impact of the PTA (Walker et al., 2013; Cottriall et al., 2009), side reins (Cottriall et al., 2009), resistance band training (Andersen et al., 2011) and raised poles (Brown et al., 2015). However, how their use affects muscle workload, despite anecdotal claims that muscle activation and hypertrophy occurs when training aids are used within equine training and rehabilitation regimes, is yet to be fully understood. The preliminary study reported here investigated if the PTA affected equine core muscle (represented by rectus abdominus) workload. This work was presented at the 13th International Society for Equitation Science conference in Wagga, Wagga, Australia 2017.

The Pessoa Training Aid™ (PTA)

The PTA is commonly used in equestrian training as a controlled method to improve strength in young or weak horses with muscular hypotrophy as a result of pathology or lack of training (Odendaal, 2009). The system consists of ropes and pulleys that run along the side and around the hindquarters of the horse (Figure 1). The aid is commonly used to create a shift in weight-bearing from the forelimb to the hindlimb, with the aim to create spinal flexion and engagement of the hindquarters to strengthen the spinal and abdominal muscles, including Rectus abdominus (RA). The cranial aspect of the PTA moves through the bit to alter the head and neck position (HNP) and create spinal flexion (Cottriall et al., 2009; Walker et al., 2013), whilst the caudal aspect of the PTA runs behind the hindquarters of the horse. The PTA can be put into three different positions: low which attaches in between the forelimbs (position one), middle which attaches at shoulder level (position two) and high which attaches in level with the withers (position three).

Position one produces a low HNP, position two an elevated HNP, and position three an extremely elevated HNP, only suitable for horses with advanced training. All positions aim to get the bridge of the nose in line with the vertical with the aim to optimise kinematic and kinetic outcomes at different stages of training. In all positions, the caudal aspect of the system with the hindquarter strap remains in the same place (Pessoa Training Aid, 2012). The proposed benefit of the hind quarter strap is to facilitate engagement of the hind limb through encouraging hind limb protraction (the swing phase of the limb where the hindlimb moves forwards towards the horse’s head). Walker and colleagues (2013) reported findings of significantly increased dorsoventral displacement of the mid-back (flexion or raised back) and lumbosacral angle at maximal hind limb retraction (the swing phase of the limb where the hindlimb moves backwards towards the horse’s tail) when horses were wearing the PTA in the middle position compared to no PTA, suggesting the aid does create improved hind limb engagement. Tension of the hind quarter strap at hind limb retraction is also likely to provide a sensory cue for the horse, with the response of increased protraction (Walker et al., 2013). Therefore, the hind quarter strap could act as a sensory aid which stimulates the sensory modulation system to encourage the horse to move the hindlimb promoting the desired effect of increased hind limb engagement (Walker et al., 2013).

Use of the PTA in the middle position (at shoulder height) has been shown to affect horses’ gait characteristics on a circle in trot. Walker’s research group (2013) found the aid significantly reduced speed, stride length and head angle when horses were lunged on a circle compared to lunging without the aid supporting the industry perspective that the aid slows a horse’s natural rhythm and facilitates increased collection and engagement However, interestingly the application of the PTA did not increase muscle activity of the superficial muscle of the back (longissimus dorsi) in trot suggesting that the aid ‘works’ by altering the function of deeper back or the abdominal musculature (Cottriall et al., 2009). The PTA is used by equestrian trainers in training and rehabilitation regimes with the aim to build and strengthen the back muscles and hindquarters in young or weak horses, through engaging the horse’s ‘core’ muscles, although this has not been studied to date. Rectus abdominis (RA) is a key ‘core’ muscle in the horse, it arises from the 4th to 9th costal cartilages and adjacent parts of the sternum, and inserts into the prepubic tendon. The muscle supports the

abdominal viscera and aids with lateral flexion and flexion of the back and limits passive excessive extension of the spine in the horse (Zsoldos et al., 2010). RA has a biphasic action and is activated initially during the stance phase at periods of low back muscle (longissimus dorsi) activation (Licka et al., 2009), the muscle then produces a second, smaller contraction at the end of stance (Zsoldas et al., 2010). These results suggest RA plays a role in arching or flexing the back, as well as providing resistance to passive extension as a result of the gravitational effects of the visceral mass (the horse’s organs) via eccentric activation (as it increases in length), making this muscle ideal to evaluate potential effects of the PTA.

Seven horses of variable breed, sex, age and height participated in our study. Prior to taking part, all horses were checked to ensure they were free from pain, healthy and sound by an experienced ACPAT registered veterinary physiotherapist. Horses also had to be used to working on the high speed treadmill and in regular exercise.

Horses had their normal bridles and rollers fitted, and markers were placed on the hindlimb to enable stride length to be measured. Electromyography (EMG) sensors were secured to the horse’s left and right RA to enable muscle workload to be measured (Figure 2). All horses then completed a warm up on the treadmill in walk, followed by three periods of data collection (Zsoldos et al., 2010; Cottriall et al., 2009):

no PTA to collect a baseline for RA activity in walk and trot

with the PTA fitted in the low position in walk and trot

with the PTA fitted in the middle position in walk and trot

The treadmill was used to ensure a standardised environment, by providing the same surface, keeping horses working in a straight line and most importantly allowing us to work them all at the same consistent speed, as speed would affect muscle workload. We then compared the different muscle workload in left and right RA muscles when horses were wearing the PTA to the baseline RA activity without the PTA on the treadmill, to see if differences existed.

In walk, minimal differences in RA activity between the baseline, no PTA condition, and walking with the PTA in the low or middle positions were found. Left RA workload increased by less than 1% with the PTA and right RA workload reduced by 1% in the low position and by 4% in the middle position, across all horses. Unsurprisingly, statistical testing found no significant differences in workload occurred (P>0.05). Using the PTA in both positions did increase the majority of horses’ left RA activity by a small amount in trot compared to when horses worked without the PTA on the treadmill. In trot, left RA workload increased by 10% in the low position and 5% in the medium position, but for right RA, workload reduced by 4% in the low position and 2% in the middle position. However, statistical tests found these differences to not be significantly different from the control (no PTA) position and could just have occurred by chance (P>0.05). These results suggests the PTA when used in the low or middle position, does not increase RA workload in walk and trot on a high speed treadmill.

It is well documented in previous research that speed can significantly affect muscle activity (Crook et al., 2010). To enable speed to be standardised, a high speed treadmill was used. Variations in stride characteristics between treadmills and over ground work have been reported including increased stance duration (SD) in the forelimbs (MendezAngulo et al., 2014). Changes in stride characteristics were observed here and interestingly this effect appeared to still apply when the PTA was utilised. In contrast, Walker and colleagues (2013) observed no change in SD when the PTA was applied during over ground analysis, suggesting the use of the treadmill impacted how the PTA works. A possible explanation for these differences could be the impact of speed. Walker and colleagues (2013) reported significant reductions in speed when the PTA was applied, however in the current study, speed was consistently maintained, preventing the horses from slowing down when wearing the PTA. As a result of this, the reduction in SD here may represent horse’s adapting to working on the treadmill in a PTA to maintain speed, suggesting the treadmill impacted on the ‘normal’ action of the PTA.

So should we use the PTA?

Our results are not conclusive and more research is needed to determine the full effect of the PTA. As well as the changes observed in SD, we noticed that when horses worked on the treadmill, they did not extend their head and neck position as low as they would when working overground in the low position of the PTA (Figure 3). This is due to the location of the breast bar on the treadmill which needs to be in place to prevent the horse moving too far forward when working on it. As a result, horses’ head position was restricted and they may not have been working in a ‘true’ outline for the low position of the PTA which would affect RA activity.

Based on our results, we would not recommend using the PTA when working horses on a treadmill but as this aid is used predominately during lunging, further research measuring RA workload during lunging is needed to explore its effect in this context.

We would like to thank Hartpury Equine Therapy Centre, and the horses and their owners who supported this study.